This invention relates to a shaft for an open-end spinning rotor, the free end of which is equipped with a supporting element which forms an essentially radially extending supporting surface for a vibrating ball of a step bearing.
It is known (German Patent Document DE 27 16 573 A1) to support the shaft of an open-end spinning rotor in the axial direction on a ball of a step bearing which is held in such a manner that it is caused to carry out vibrations of low amplitudes and of a high frequency. The free end of the shaft is equipped with a lengthening which has a reduced diameter and is used as a supporting element abutting the ball of the step bearing. The low amplitude vibrations have the result that the position of the shaft and therefore of the opened spinning rotor does not change noticeably. In addition, the vibrations have the result that the ball is supported on continuously changing supporting points on the supporting surface of the shaft and on an opposite abutment so that the ball carries out rotational movements. Since the ball is wetted with lubricant, a low-wear bearing is obtained despite the high rotational speeds which today are at 100,000 min.sup.-1 (revolutions per minute) and higher.
The open-end spinning rotor is a wearing part that has to be exchanged after an extensive operating time. As a result of improvements of the rotor and particularly by applying comings to the rotor, it has been achieved that a relatively long life was obtained for the rotor. The relatively long life of the rotor has the result that today different wear phenomena become noticeable on the open-end spinning rotor assembly and influence the overall life time. When the life time of the rotor and therefore the running time is increased and, in addition, the rotational speeds of the rotor are extremely high, it is found that the vibrations of the ball of the step bearing result in a deformation of the supporting element in the area of its supporting surface so that over time the supporting element is axially shortened. This shortening takes place before the rotor exhibits such manifestations of wear that an exchange of the open-end spinning rotor is necessary. These shortenings of the supporting element have the result that the rotor changes its position in the spinning arrangement to an unacceptable extent. Actually, it would easily be possible to compensate this change of position by an axial readjusting of the abutment of the step bearing ball. However, this is not very useful in the case of machines used in practice because these machines have two hundred and more spinning positions, and because the open-end spinning rotor assemblies are to be exchangeable with respect to one another.
In order to solve this problem of the shortening of the shaft of the open-end spinning rotor, it was suggested in a German Patent Application (P 40 20 411.1), which is no prior publication, to arrange an exchangeable supporting element on the free end of the shaft which forms an exchangeable wearing part. This exchangeable element is arranged in a centric bore of the shaft so that an exchange does not have the result that the open-end spinning rotor assembly must be newly adjusted. The supporting element, which is used as the wearing part, projects out of the free end of the shaft in such a manner that a tool can be applied for the pulling-off of this supporting element.
For the solution of the problem, it was suggested in another German Patent Application (P 40 37 833.0), which is no prior publication, to mount a supporting element in the form of a small plate on the free end of the shaft, in which case a damping layer may be provided between the supporting element and the shaft.
In the case of another type of bearing of an open-end spinning rotor assembly, it is known (German Patent Document DE 19 01 453 A1) to support the free end of the shaft against a step plate which is held in a receiving plate made of an elastic material so that the transmission of vibrations is prevented. In the case of this construction, it is known to arrange at the free end of the shaft a particularly hard supporting device which may be made, for example, of a hard metal, of a diamond or of a ceramic material. This supporting device is to be fastened to the shaft in a fixed manner, for example, by means of a press fit or by crimping, or in an exchangeable manner. The supporting device has a hemispherical shape so that it is supported on the step plate approximately in a punctiform manner.
It is an object of the invention to develop a shaft of the initially mentioned type in such a manner that a deforming in the area of the supporting surface of the supporting element is reduced significantly so that the supporting element, despite very high rotational rotor speeds, is not the reason why the open-end spinning rotor assembly becomes unserviceable.
This and other objects are achieved by the present invention which provides a shaft assembly for an open-end spinning rotor comprising a shaft having a first end supporting a rotor and an opposite second face end that has a diameter reduced relative to the shaft approximately 0.6 times. The assembly includes a receiving device at the free end of the shaft, and a substantially cylindrical ceramic supporting element pressed into the receiving device. The supporting element has a supporting surface projecting slightly out of the receiving device of the shaft in the axial direction. The supporting surface and the supporting element have diameters that correspond to approximately half of a radius of a vibrating bell to which the supporting surface is applicable. The supporting surface has rounded edges with a radius approximately 1/10 of the diameter of the supporting element.
By means of the development according to the invention, it is important to use a supporting element that is made of materials of a very high hardness although, in comparison to steel, these materials are relatively brittle and therefore sensitive to impacts. A destruction of such a supporting element is probably prevented by the fact that this supporting element is laterally bordered by the shaft, particularly near the area of its supporting surface. In this case, the centric mounting of this supporting element has the advantage that the supporting element cannot result in any significant unbalanced mass even if its specific weight deviates significantly from the specific weight of the shaft which is made of a steel type. The balancing of the open-end spinning rotor assembly is therefore not made more difficult by such a supporting element.
In a further development of the invention, it is provided that the supporting element and the receiving device each have a cylindrical shape. In a particularly simple manner, this results in a precisely centric arrangement. It is also advantageous in this case that, in a further development of the invention, the axial length of the supporting element corresponds to approximately 2 to 3 times its diameter. As a result, a secure centric position is achieved. A secure protection against a breaking-out of the material of the supporting element in the edge areas is obtained when, in a further development of the invention, the outside diameter of the shaft in the area of the receiving device corresponds to approximately twice the diameter of the receiving device.
In a further development of the invention, it is provided that the supporting element is held in the receiving device in a ring-shaped manner in the axial direction on its end facing away from the supporting surface. Probably this measure also promotes the fact that the supporting element which is brittle per se is not destroyed by the vibrating ball of the step bearing since the supporting element is free for the most part in the axial direction on the side situated opposite the supporting surface so that it can vibrate or swing in the axial direction.
In an advantageous development of the invention, it is provided that the supporting element is made of a ceramic material. Although such ceramic materials and particularly oxide ceramic materials are very brittle and have only a relatively low resistance to impact, supporting elements made of such a material have exhibited particularly good results in tests with respect to their resistance to wear.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.